In recent years there continues to be dramatic density increases in integrated circuit technology. For example, the minimum feature size of lithography, such as the size of MOSFETs, has been reduced to one micrometer and below. In the fabrication of precision capacitors in conjunction with FET devices on the same chip at these reduced dimensions, it is increasingly difficult to maintain such parameters as low voltage and temperature coefficients and low leakage current.
Among typical integrated circuits, some circuit components are designed and manufactured to operate at high voltages (e.g., 3.3 V), while others are designed and constructed to operate at low voltage 1.8 V. However, since low voltage MOSFETs are typically less expensive to manufacture, and in many cases are already present in existing circuit patterns, it is desirable to employ low voltage MOSFETs in place of high voltage MOSFETs in as many application as possible. In addition, MOSFETs have in some cases been employed for use as other devices, rather than as transistor devices. For example, many circuit designs have employed the capacitive properties of MOSFETs to form capacitors in integrated circuits without the need to specifically manufacture capacitors for these uses. When employed, such approaches can significantly reduce the manufacturing time and overall costs of forming integrated circuits.
Unfortunately, many conventional applications for MOSFETs employed in this manner are operated under high voltage, thus typically requiring the use of high voltage MOSFETs (i.e., thicker gate dielectrics to achieve higher breakdown voltage) rather than low voltage devices. Since the use of high voltage MOSFETs typically increases overall manufacturing costs, as mentioned above, the capability of employing low voltage devices in high voltage circuits would be advantageous in many respects. A particular benefit would be the use of such low voltage MOSFETs in place of capacitors where many such MOSFETs are readily available (and perhaps are not being used in the particular circuit design), obviating the need to specifically form high voltage MOSFETs or specialized capacitors.